The phoney war is over: tomorrow the Office of Fair Trading takes on eight banks in the High Court to settle – once and for all – the issue of whether current account penalty charges are fair.

Fearful of a hefty future loss of current account income, banks have recently begun to tweak the way that they charge for overdrafts and, in the process, turned the task of working out charges into a complicated and testing ordeal for many customers.

New research from data analyst Moneyfacts reveals how an unauthorized breach of overdraft to the tune of £100 – one that you subsequently take 14 calendar days to pay back – can cost you vastly different sums depending on your bank.

It discovered that the cheapest is HSBC's bank account, at £25.72, and the most expensive is Lloyds TSB's Classic Plus account at £165.72. As a point of comparison, Nationwide building society's Flexaccount charges £42.46 and Halifax's high interest current account £64.10.

Towards the end of last year, both Alliance & Leicester and Lloyds TSB abandoned their old charges on unauthorised overdrafts for a new fee 'scale' that left many consumers confused . For example, A&L dropped its combination of a 5.9 per cent unauthorised overdraft interest rate and £25 penalty fee (capped at £50 a month) for a flat £5 per day; and it is uncapped, so you could pay as much as £155 a month for an indiscretion.

Elsewhere, First Direct told customers they would no longer receive interest on their current accounts, but that it would instead cut the cost of emergency unauthorised borrowing .

'Such changes have been so confusing – something needs to happen [with the test case] so that the market can move forward from this,' says Kevin Mountford, head of current accounts at price comparison site Moneysupermarket.com. 'Worse, there has been a lull in the current account switching market because of the OFT [case]. '

The latest switching figures from another price comparison website, Moneyexpert.com, suggest that current accounts remain one of the most 'sticky' and apathetic products for consumers. It shows that only 5 per cent of people had switched bank accounts in the previous six-month period compared with 15 per cent for electricity and car insurance, 13 per cent for gas, 12 per cent for credit cards; 11 per cent for broadband; and 10 per cent for home insurance. Only mortgages (4 per cent) and personal loans (2 per cent) were lower.

Those prepared to switch current accounts want a cheap overdraft (if they spend a great deal of time in the red) or decent credit interest (if they stay in the black). Abbey is offering 8 per cent interest on balances up to £2,500 to switchers looking for credit interest, Mountford says, but the interest drops to 2.5 per cent after 12 months . For those always in credit and earning more than £15,000, Moneysavingexpert.com, a consumer revenge website, backs the Alliance & Leicester Premier Direct Online current account which pays 6.5 per cent on balances of up to £2,500, falling to 4.75 per cent a year later.

If you are always overdrawn, Money facts' best-buy tables recommend the same A&L account because of its 0 per cent authorised overdraft for 12 months followed by its new 50p-a-day regime (to a maximum of £5 a month), and Halifax's Moneyback account, charging 6.9 per cent.